[Coco] [Color Computer] The evolution of the Coco..

[j_e_daggett]

Actuall it is true. All the external circuitry needed is a 74LS161 and
 the EPROM. The 161 serves as a row counter for the EPROM. Three
signals from the 6847 are pbrought to the LS161. They are RP, FS, and
 HS. They tie to teh LS161 in this order. MR, PE, and CP.  The Q
outputs of the LS161 form the row address. 

The MC6847 can alternate characters on the screen from internal and
external character generator. There is a pin on the MC6847 that is
labeled INT/EXT and thta controls whether you use internal  or
external character rom/ram.

james


--- In ColorComputer at yahoogroups.com, Mike Pepe <lamune at d...> wrote:
> 
> 
> James Diffendaffer wrote:
> > 
> > The CoCo 1/2's VDG does support the use of an external ROM for it's
> > character set.  
> 
> Actually that's not true.
> 
> The 6847 does support an external character generator. It's fairly 
> trivial and only requires a couple of chips in addition to a ROM/EPROM 
> containing the new character set.
> 
> I think Green Mountain Micro made a little adapter card you stuck in
the 
> 6847 socket and gave you real lower case. LowerKit(?) I thought. Maybe 
> it's in one of my old Rainbow mags.
> 
> > I don't see why someone shouldn't do it.  So what if it's slow.  If a
> > faster CoCo becomes available in the future if could run fast enough.
> > 
> 
> I'd like to see a faster CoCo in the future. The stuff Cloud9 is doing 
> is impressive but I think it might be in the wrong direction.
> 
> The "C-64 on a chip" is probably the better direction to go.
> 
> Emulating the CoCo on some CPLD devices releases us from reliance on
the 
> old chips and hardware which- while not rare- are no longer in
production.
> 
> In addition all these plastic packaged chips in our CoCos are slowly 
> degrading. Not sure how long it takes but they're not hermetically 
> sealed and will eventually oxidize.
> 
> Just my opinion.
> 
> -Mike





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